coupling clutches and brakes

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COUPLINGS CLUTCHES AND BRAKESBranch : Chemical EngineeringGroup=4Coupling and Clutches are power transmission elements. It is used for transmitting power from one shaft to the another. A Brake is a frictional device whose primary function is to control the motion of the machine member. INTRODUCTION:- -:Coupling:-

A coupling is a device used to connect or couple two shafts. Shafts are mostly available up to 7 meters length due to transport difficulty. To get a greater length , it is necessary to joint two or more pieces of the shaft using coupling.Shaft coupling are used in machinery for following purposes:To connect shafts of motor and generator which are manufactured separately and to provide for disconnection for repairs or alternations.To reduce the transmission of shock loads from one shaft to another.To allow misalignment of the shaft or to introduce mechanical flexibility.To introduce protection against overloads.

Types of couplingsSleeve or muff couplingIt is made from cast iron and very simple to design and manufacture. It consists of a hollow cylinder whose inner diameter is the same as diameter of the shaft.The hollow cylinder is fitted over the end of the two shafts with the help of taper sunk key.A key and sleeve useful to transmit power from one shaft to the other shaft.The main disadvantage of this coupling is that it is difficult to assemble when there is no perfect alignment between shafts.

Sleeve or muff coupling

Clamp or split muff or compression couplingIn this coupling , the muff or sleeve is made into two halves parts of cast iron and they are join together by means of mild steel studs and nuts.The advantages of this coupling is that assembling of the coupling is possible without change the position of shaft.This coupling is used for heavy power transmission at moderate speed.Clamp or split muff or compression coupling

Flange couplingThis coupling is having two separate cast iron flanges.Each flange is mounted on the shaft end and keyed to it.This coupling prevent catching clothes of workman.This flange couplings is most accurate and rigid.It is used for heavy power transmission at low speed.Flange coupling

Bush pin type flange couplingThis is modified form of protected type flange coupling. This type of coupling has a pins and it work as a coupling bolts.The rubber or leather bushes are used over the pins.This coupling is used to connect of shafts which having the small parallel misalignment, angular misalignment and axial displacement.This type of coupling is mostly used to couple an electric motor and machine.Bush pin type flange coupling

Universal couplingUniversal coupling consists of two similar forks keyed on the ends of the two shafts.This coupling is used to connect two shafts whose axis intersect.It also used to connect two shafts, where the angle between two shafts may be varied when they rotate.It is widely used in automobile and machine tools.Universal coupling

Oldhams couplingIt consist of two flange and a central floating disc.This coupling is used in connecting two parallel shafts but not in alignment, and their axis are at small distance apart.Oldhams coupling

Clutches

Clutch is a one of the form of coupling. Clutches is used to transmit the power from driving shaft to driven shaft of machine which may be required to start or stop frequently.It is so designed that the two members may be engaged or disengaged whenever required either by a hand operated device or automatically by the action of some power driven devices.Types of clutchesDisc clutchesThis type of clutch consists of two flanges, one flange is rigidly to the driving shaft and other flange fitted to the driven shaft.Single disc clutches are used in automobiles.When large torque transmission is required the multi disc clutch are used.Multi disc clutch has more number of contact surfaces discs on driving and driven shaft.

Disc clutches

Cone clutchThe cone clutch consists two cones , one internal cone fixed to the driven shaft and another cone fitted on the driven shaft.The operating lever used only for disengagement of the clutch.The main advantage of cone clutch over the disc clutch is very simple and required less axial pressure to disengaged the clutch.Cone clutch

Centrifugal clutchIt consists of a number of shoes on the inside of a drum or rim of the pulley.The upper surface of the shoes are covered with a friction material.The spider is fitted on the driving shaft.When centrifugal force is equal to spring force, the shoe is just floating.But, when centrifugal force higher than the spring force, the shoes moves outward and comes into contact with the driven member and pressure against it.The increase of speed causes the shoes to press harder and clutch transmit more power.Centrifugal clutch

Positive Contact ClutchIt is consists of segmental projections on one of the flange and corresponding recesses on other flange on the driven shaft.Driving flange rigidly keyed to the driving shaft while the other flange is keyed to driven shaft by splines so that it can slide on that shaft.The sliding flange engage with the fixed flange to transmit the motion and power from driving shaft.This clutch is used for the transmission of power in agricultural equipment like tractor, thresher, etc.Positive Contact Clutch

Brakes

A brake is a mechanical device which produces frictional resistance against moving machine member, in order to slow down the motion of machine. In the process of performing this function, the brake absorbs kinetic energy of moving member and the brake absorbs potential energy of lowering member.The energy absorbed by brakes is released to surrounding in form of heat.Types of brakesBlock brakeSingle block or shoe brake:A single block is consists of a block which is pressed against the rim of revolving brake wheel drum.This brake is used in railway trains and tram cars.The prony brake is example of block brake.Single block or shoe brake:

(2) Double block or shoe brake:

It consists of two brake blocks at the opposite ends of the wheel. These shoes apply force to both sides of wheel and reduces the unbalanced force on the shaft. The spring pulls the upper end of brake arms together and brake is applied. When a force is applied to the bell crank lever, the spring is compressed and the brake is released. This brake is used on electric cranes. The bicycle brake is example of double block brake.

Double block or shoe brake:

Band brakeA band brake consists of a flexible steel band lined with friction material, which wrap to the brake drum.When an upward force is applied to the lever end, the lever turns about the fulcrum pin and tightens the band on the drum and hence the brakes are applied.The friction between the band and the drum provides the braking force.This type of brake is used in civil construction equipment and also in automobiles as hand brake.The rope brake is example of band brake.Band brake

Internal expanding shoe brakeAn internal expanding shoe brake consists of two shoes.The outer surface of the shoes are covered with friction material.Each shoe is pivoted at one end about a fixed fulcrum and other end rests against cam.When the cam is operated, the shoe are pushed outwards against brake drum.The friction between the shoes and the drum produces the braking torque.This type of brake is commonly used in motor cars and light trucks. Internal expanding shoe brake

Difference Between A Brake And A ClutchA brake is used to slow down or stop the motion of a moving body, whereas a clutch is to transmit the motion of a moving body to another body by means of engagement.In a brake , the force applied is converted into frictional resistance , while in a clutch the force is not converted into frictional resistance except in case of slip.A brake always remains disengaged and may be engaged when required whereas a clutch always remains engaged.

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